The present invention relates to an optical filter comprising a transparent support and a filter layer. In more detail, the invention relates to an optical filter covering a display surface of a display device such as a liquid crystal display device (LCD), a plasma display panel (PDP), an electroluminescence display (ELD), a cathode-ray tube (CRT), a fluorescent indicator tube or a field emission display to improve the color reproducibility of the display.
A display device such as a liquid crystal display device (LCD), a plasma display panel (PDP), an electroluminescence display (ELD), a cathode-ray tube (CRT), a fluorescent indicator tube or a field emission display displays a color image with a combination of the three primary colors (i.e., red, blue, green). However, it is very difficult (substantially impossible) to use the ideal three primary colors. For example, the plasma display panel (PDP) uses phosphors of the three primary colors, which emit light containing an unnecessary component (in the wavelength region of 500 to 620 nm). Therefore, an optical filter absorbing the unnecessary component has been proposed to correct the color balance of the displayed image. The optical filter for the color correction is described in Japanese Patent Provisional Publication Nos. 58(1983)-153904, 60(1985)-118748, 60(1985)-18749, 61(1986)-188501, 3(1991)-231988, 5(1993)-203804, 5(1993)-205643, 7(1995)-307133, 9(1997)-145918, 9(1997)-306366 and 10(1998)-26704.
Only a light component that impairs color purity must be selectively cut off to correct a color balance of a displayed image. The present inventors, however, have found that conventional optical filters often cut off not only the light component impairing the color purity but also a component contributing toward displaying the image.
An object of the present invention is to provide an optical filter having a function of correcting color appropriately for a displayed image.
Another object of the present invention is to provide an improved plasma display panel, which can give an image having appropriately corrected colors.
The present invention provides an optical filter which comprises a transparent support and a filter layer, wherein the filter layer has an absorption maximum in the wave-length region of 560 to 620 nm, and the absorption maximum has a half-width in the range of 5 to 50 nm.
The invention also provides a plasma display panel having a display surface covered with an optical filter which comprises a transparent support and a filter layer, wherein the filter layer has an absorption maximum in the wavelength region of 560 to 620 nm, and the absorption maximum has a half-width in the range of 5 to 50 nm.
The present inventors have studied a display device (particularly, a plasma display panel), and found that the unnecessary light component (in the wavelength region of 500 to 620 nm) contained in the three primary colors gives an emission spectrum with a very sharp peak. Accordingly, the optical filter for cutting off the unnecessary component must have an absorption spectrum with a very sharp peak corresponding to the above sharp emission peak. If the filter has a broad absorption peak, it cuts off the necessary component contributing towards displaying the image.
The optical filter of the invention has an absorption spectrum with a very sharp peak (whose half-width is in the range of 5 to 50 nm), and hence it can selectively cut off the light component impairing the color purity of image.
Therefore, the color of the displayed image can be appropriately corrected by the optical filter of the present invention.